1. Field of the Invention
The present invention relates to a hydraulic brake apparatus for a vehicle, and more particularly to the apparatus having an auxiliary pressure source for generating a brake pressure and a valve assembly for regulating the brake pressure.
2. Description of the Related Arts
A hydraulic brake apparatus having an auxiliary pressure source as disclosed in the U.S. Pat. No. 5,515,678 is adapted to provide a brake pressure generating device which can alter a characteristic of a pressure in a pressure chamber relative to a brake pedal operating force. This brake pressure generating device includes a cylinder body, a pressure source connected with the cylinder body for generating a pressure, a piston slidably disposed in the cylinder body for being operated by a brake pedal of the vehicle, a spool valve slidably disposed in the cylinder body for forming a pressure chamber with the piston at one end thereof and for regulating the pressure of the pressure source, and restriction means which receives a regulated pressure from the spool valve at one end thereof and connected with the other end of the spool valve at the other end thereof for varying a characteristic of a relation between a pressure in the pressure chamber and the regulated pressure.
In the above-described brake apparatus, by changing the outer diameter of the piston slidably received in the sleeve, and the outer diameter of the restriction means connected with the spool valve, it is possible to alter the regulated pressure in accordance with the pressure generated in the pressure chamber. According to the above-described brake apparatus, however, the spool is arranged to receive every force to be regulated. Therefore, it is necessary to make the spool by high-intensity material. This will be a great bar, when the apparatus is to be made small, and its manufacturing cost will be raised.